Sunday, 1 May 2022

Crisis? What Crisis? Scientists Work Out How Mitochondria Evolved

A white blood cell ingests rod-shaped bacteria (pink) in this micrograph. Legionella bacteria probably evolved to exploit this system about 2 billion years ago.
Ancestors of legionella bacteria infected cells two billion years ago | Press release - Uppsala University, Sweden

One of the mysteries of evolutionary biology was how and when complex (eukaryote) cells acquired mitochondria. Now scientists at Upsala University, Sweden, believe they have solved that problem.

They have discovered that, soon after eukaryotes began to feed on bacteria by phagocytosis (swallowing them whole and digesting them internally) the ancestors of legionella bacteria evolved the ability to exploit this system and live as parasites inside the cells, as early as two billion years ago.

They also believe they have solved one of the chicken-and-egg conundrums in evolutionary biology - which came first, phagocytosis, which requires energy to digest the phagocytosed organisms, or mitochondria, which supply the cell with energy. Some scientists believe that the cell would need mitochondria to supply enough energy for phagocytosis. However, this finding appears to show that phagocytosis was the process by which mitochondria were acquired. This of course, explains why eukaryotes soon evolved a symbiotic relationship from what almost certainly began as a host-parasite relationship. The benefits were so great.

The Upsala team published their findings, open access, in the journal Molecular Biology and Evolution last February.


A eukaryotic cell uses phagocytosis to eat a smaller cell in this video. The development of this ability was an important evolutionary innovation for eukaryotes.
Wim van Egmond

We discovered that the ancestor of the whole group lived about two billion years ago, at a time when eukaryotes were still in the making, evolving from simpler cells to the complex cell structure they have now. We believe Legionellales were among the first to infect eukaryotic cells.

Andrei Guliaev, co-author
Department of Medical Biochemistry and Microbiology
Science for Life Laboratories
Uppsala University, Uppsala, Sweden
The legionella are a very large group of bacteria which includes the bacterium that causes legionnaires disease. All have the ability to infect eukaryote cells such as amoebae, insects and us.

From the Upsala University press release:

Some researchers believe that mitochondria were required to deliver enough energy for phagocytosis to work. But our results suggest that phagocytosis came first – two billion years ago – while mitochondria came later

Lionel Guy, co-author
Department of Medical Biochemistry and Microbiology
Science for Life Laboratories
Uppsala University, Uppsala, Sweden
The first step in an infection with legionella bacteria is for a eukaryotic host, such as an amoeba, to bring the bacterium into its cell through a process called phagocytosis. The next step for the amoeba would be to digest the bacterium and use its parts as an energy source. But legionella bacteria have molecular tools that keep them from being digested and allow them to instead use the amoeba as an energy source so they can multiply.

In the study, the researchers show that all Legionellales have the same kind of molecular tools as legionella. That suggests that the ability to infect eukaryotes already existed in the ancestor of all Legionellales. This means that phagocytosis is at least as old as Legionellales – two billion years old – when eukaryotes were in the early stages of their evolution.

Which has implications for a hot chicken-or-egg debate in evolutionary biology about how eukaryotes came into being. Which came first? Was it the mitochondria, which originated from another group of bacteria and became our cells’ own energy factories? Or was it phagocytosis, which is considered necessary to absorb mitochondria but is very costly from an energy standpoint?
Copyright: © 2022 The authors. Published by Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.
Open access
More detail is given in the abstract to the Molecular Biology and Evolution paper:
Abstract

Bacteria adapting to living in a host cell caused the most salient events in the evolution of eukaryotes, namely the seminal fusion with an archaeon, and the emergence of both mitochondrion and chloroplast. A bacterial clade that may hold the key to understanding these events is the deep-branching gammaproteobacterial order Legionellales—containing among others Coxiella and Legionella—of which all known members grow inside eukaryotic cells. Here, by analyzing 35 novel Legionellales genomes mainly acquired through metagenomics, we show that this group is much more diverse than previously thought, and that key host-adaptation events took place very early in its evolution. Crucial virulence factors like the Type IVB secretion (Dot/Icm) system and two shared effector proteins were gained in the last Legionellales common ancestor (LLCA). Many metabolic gene families were lost in LLCA and its immediate descendants, including functions directly and indirectly related to molybdenum metabolism. On the other hand, genome sizes increased in the ancestors of the Legionella genus. We estimate that LLCA lived approximately 1.89 Ga, probably predating the last eukaryotic common ancestor by approximately 0.4–1.0 Gy. These elements strongly indicate that host adaptation arose only once in Legionellales, and that these bacteria were using advanced molecular machinery to exploit and manipulate host cells early in eukaryogenesis.

Hugoson, Eric; Guliaev, Andrei; Ammunét, Tea; Guy, Lionel
Host-adaptation in Legionellales is 1.9 Ga, coincident with eukaryogenesis.
Molecular Biology and Evolution, 2022, DOI: 10.1093; 10.1093/molbev/msac037

Copyright: © 2022 The authors. Published by Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.
Open access
Reprinted under a Creative Commons Attribution-NonCommercial 4.0 International license (CC BY-NC 4.0)
Once again then we see a piece of science research which utterly refutes the increasingly forlorn claim by creationists that the TOE is a scientific theory in crisis, about to be overthrown and replaced, for the first time in history, by one based on primitive superstitions. A childish superstition involving an imaginary supernatural entity which has never been shown to exist or do anything, and a mechanism for whose existence or modus operandum has never even been demonstrated.

Simply by revealing the demonstrable facts, creationism has been refuted yet again. One day surely, creationism as a movement is going to have to face up to the fact that it has no scientific basis and abandon the ludicrous pretence to be a serious alternative science.

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